Introverts and Leading Functions

Why is that a lot of people think that IXXJs should have leading judging functions and IXXPs should have leading perceiving functions? If IXXJs had a leading judging function, wouldn't they apear as perceiving to the outside world because of the hypothetical extroverted perceiving functions. If IXXPs had a leading perceiving function, wouldn't they appear as judging to the outside world because of their extroverted judging functions?